Hello. When you say they go to a local waterbody, do you mean a particular waterbody you want surveyed, or do you mean they go to any waterbody they like?
The Field Studies Council here in UK initiated a citizen science pond survey about ten years ago which allowed users to categorise their pond as poor, medium or rich. It is probably on their website somewhere, but the taxonomic level was so low and the threshold for rich was so low, I wouldn’t recommend it.
As far as collecting time goes, this literature review, done about 20 years ago, might help. I can e-mail the full report if you want, but it is a mixture of Word files and Excel files. (CCW = Countryside Council for Wales, the government conservation body now extinct through hybridisation.)
CCW has an interest in methods of monitoring the aquatic invertebrates of ditches for two reasons. Firstly the numerous commercial developments in the Gwent Levels are preceded by environmental impact assessments which often concentrate on the ditch fauna and there is a need to establish an efficient standard method for these assessments. Secondly, CCW has an obligation to monitor whether the Gwent Levels are continuing to support a rich aquatic fauna, as this fauna contributed to the area qualifying as SSSIs. To carry out monitoring of ditch invertebrates, a collecting method is needed which is effective enough to take most target species, efficient enough that it takes only a short time (ideally allowing several ditches per day to be sampled), and simple enough that different people can carry it out and get consistent results.
There is a recommended method for monitoring the aquatic invertebrates found in Gwent Levels ditches (CCW 1996), consisting of six standardised net sweeps from the bank towards the ditch centre using a standard pond net, followed by 10 minutes sorting the contents in a white tray. The whole procedure is duplicated at each sampling station so the collection at one site is derived from 12 net sweeps. The recommended period for such sampling is between mid-May and mid-June or in late September. This study was intended to test whether the twelve net sweeps caught all or most of the target invertebrates (limited to aquatic beetles and aquatic bugs in this study, see below), whether a less formal collecting procedure using a sieve was more efficient, and whether the months recommended by CCW were the best times of year. It forms part of work to find a ditch monitoring method for the Gwent Levels SSSIs. Because of the difficulties in travelling regularly from Bangor to Gwent, the study was carried out in another grazing marsh close to Bangor, the Malltraeth Marsh SSSI and RSPB reserve on Anglesey.
The question of how to sample water beetles in a scientific way has been addressed several times. Landin (1976a, 1976b) studied the beetle families Hydrophilidae and Hydraenidae in a mud-bottomed lake in Sweden using two sampling methods: an absolute method of taking cores from the littoral zone and extracting the beetles using a Tullgren funnel; and a relative method (catch per unit effort) of stirring the lake bed by hand and collecting beetles as they rose to the surface, carried out for 45 minutes. Landin was studying population size of individual species rather than species richness, but it is nevertheless instructive that the seasonal abundance pattern from cores could differ greatly from the catch per unit effort. For example, Hydraena britteni shows a large spring peak and a smaller autumn peak in core samples in 1965, whereas timed collecting showed virtually no spring peak and a large autumn peak. Even the “absolute” method differed in efficiency between species according to their size, extracting 90% or more of large hydrophilids but only 59% of the tiny Limnebius aluta.
In a study more similar to the present one, Jeffries (1987) repeatedly sampled eleven small freshwater ponds for water beetles in Aberlady Bay, Scotland, on eleven occasions between 22 March and 22 August. A sample consisted of a single 30 cm net sweep through the water and vegetation, which Jeffries admits is not an exhaustive sample of the pond. He found the more species-rich pools required fewer visits/sweeps to take 50% of their total species, but full species accumulation curves are not given. Combining the data from all pools, 50% of species were taken after only two visits, though some individual ponds required seven visits before 50% of their eventual total was reached.
The sampling method stipulated by Pond Action (Biggs et al. 1998) for surveying pond invertebrates consists of “vigorous netting” for a total of 3 minutes, divided equally between different habitats in the pond, plus 1 minute searching for animals which may have been missed. The whole process is repeated in spring, summer and autumn. The whole invertebrate catch is preserved and sorted in the lab and the results are treated as quantitative data. Botanical, chemical and other environmental measurements are also taken. The method was derived from extensive trials though the detailed results of the trials have not been published so the thoroughness of the methods cannot be compared with other studies. While 3 minutes of vigorous netting may seem very brief for sampling a whole pond, it must be remembered that this is the time spent with the net in the water. The six standardised net sweeps stipulated by CCW (1996) would involve the net being in the water for less than 30 seconds. Also, Pond Action’s aim was to develop a pond classification and investigate the factors influencing the composition of the pond community. They were not seeking to produce a complete inventory of pond invertebrates.
Standen (1999) attempted to find the most economical sampling protocol for estimating the abundance and taxon-richness of northern Sphagnum pools in Sutherland in order to study the effects of afforestation. The sampling method was partly related to pool size: a net sweep from every 2 metres of pool perimeter but with a maximum of 20 sweeps from any one pool. She reported that the number of taxa from any one pool did not rise after 30 individuals had been caught, though the plateau in her results could also be interpreted as a curve of gradually diminishing steepness. The habitat studied was species-poor compared to Malltraeth Marsh – 53 pools in her richest category of pool contained only 4 species of bug and 14 species of beetle in total. Even taking into account the species-poor habitat, her collecting rate of only 2.64 - 3.48 individual invertebrates (all taxa) per metre of pool perimeter suggests the collecting method was ineffective.
Savage (1981) collected corixids from a saline lake in Cheshire by using a pond net to sweep a 2 metre route three times. This constituted a standard net sweep, and was repeated ten times at each collecting site on each visit. For the most abundant species, the results were consistent enough for population peaks and troughs to be discernible though overlap in 95% confidence limits were common.
Numerous other studies have used a standard method of collecting in order to make the results from different sites “comparable” but without reporting any testing of the method for consistency or effectiveness. Macan (1938) used a hand-net to collect 20 to 30 corixids within the smallest possible area. Kirby (1983) used a triangular dredge to collect corixids from drains, calculating the number caught per metre dredged. Drake (1986), collecting in the Gwent Levels ditches, used a standard time of 1 hour during which 5-8 dips of the net were made. He describes this method as qualitative, not quantitative, being used to ensure results were not biased by greater effort being made at any particular site. Most of the hour was spent on extracting specimens from a sorting tray with five minutes at the end searching the ditch for conspicuous species. No other survey of the Gwent Levels has matched Drake’s for number of taxa taken per sampling site. Gibbs (1991) used 12 net sweeps and 20 minutes of sorting, which is the basis for the recommendations by CCW (CCW 1996). Jackson (1997) reviewed sampling methods for invertebrates in shallow water, discussing various types of trap, artificial substrates, mechanical grabs and the hand-net. The hand-net is highly recommended (p. 122), even though it is selective and suffers from inconsistency between operators. The latter problem, he suggests, can be overcome by having all surveying done by a single person - not a realistic option for long-term monitoring programmes, and even a single person would differ in technique as years passed. The other group of methods which Jackson scores highly is the laying of artificial substrates such as bundles of rope fibres or plastic aquarium plants, but these are less suitable for highly mobile species such as diving beetles and bugs, which are likely to abandon the substrate when it is being removed from the water.
The only previous extensive study of the water beetles of Malltraeth Marsh (Foster & Bilton 1985) used an arbitrary sampling method of “one minute of vigorous netting”, and had the novelty of it being repeated at most sites by two people. In 30 samples, A caught 1.2 times as many individual beetles as B but B took one more species than A. TWINSPAN analysis failed to detect any difference between the collectors, both of whom are experts at surveying water beetles.